noun \ˈkō-ˌsīn\

geometry : the ratio between the long side (called the hypotenuse) and the side that is next to an acute angle in a right triangle

Full Definition of COSINE

:  a trigonometric function that for an acute angle is the ratio between the leg adjacent to the angle when it is considered part of a right triangle and the hypotenuse
:  a trigonometric function cos θ that for all real numbers θ is given by the sum of the alternating series and that is exactly equal to the cosine of an angle of measure θ in radians

Origin of COSINE

New Latin cosinus, from co- + Medieval Latin sinus sine
First Known Use: 1635


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